This invention relates to a fuel injection nozzle for supplying fuel to an internal combustion engine, the nozzle comprising a nozzle body defining at one end a mounting face, a blind bore extending inwardly from the mounting face towards the other end of the body, a seating defined in the bore, a valve member slidable in the bore and engagable in its closed position with the seating to prevent flow of fuel from a nozzle inlet through an outlet, the valve member being movable by fuel under pressure supplied to the inlet away from said seating to allow fuel flow through the outlet, a nozzle holder, a distance piece interposed between an end face of the holder and said mounting face, means securing the nozzle holder, the distance piece and the nozzle body in assembled relationship, a first spring housed within a chamber defined in the holder, the first spring acting through a rod to urge the valve member into contact with the seating, a second spring housed within the chamber, a spring abutment engaged with one end of said second spring and a push-piece located between the valve member and said spring abutment, said valve member being initially moved by the fuel pressure against the action of the first spring to allow a restricted flow of fuel through the outlet and after a predetermined movement, against the action of both springs to allow an increased rate of flow of fuel through the outlet.
Such nozzles are well known in the art and provide what is known as two-stage lift of the valve member. The initial stage of lift may be as low as 0.06 mm and in order to achieve the desired purpose ie a reduction in the rate of rise of pressure in the engine cylinder by restricting the rate of fuel delivery, it is necessary that the initial stage of lift should be carefully controlled.
One example of such a nozzle is seen in U.S. Pat. No. 4,768,719 in which the push-piece is in the form of a flanged bush which is housed in a stepped bore in the distance piece. The spring abutment engages the bush and urges it into contact with the mounting face of the nozzle body and the bush is engaged by the valve member at the end of said predetermined movement. In the closed position of the valve member the end of the valve member therefore has to lie a distance below the level of said mounting face corresponding to said predetermined movement and it is not particularly easy to machine the valve member to the high degree of accuracy required.
Another example of such a nozzle is seen in GB No. 2188367 in which the end face of the valve member again lies below the mounting face of the nozzle body in the closed position of the valve member. In this example however the spring abutment does engage the end face of the distance piece which is presented to the aforesaid end face of the holder thereby making it easier to adjust the pre-load of the second spring.